Processing method and bearing

ABSTRACT

A processing method for a bearing is capable of shortening a lead time without the need for carrying out super finishing (mirror grinding). A component of a bearing is finished while chucking the component by a chucking device. Hardened steel cutting and grinding are carried out while chucking the component without releasing the chucking by the chucking device.

TECHNICAL FIELD

The present invention relates to a processing method of processing acomponent of, for example, a deep groove ball bearing, an angularcontact ball bearing, or a tapered roller bearing, and relates to abearing using the component processed by the processing method.

BACKGROUND ART

As a method of manufacturing a bearing ring (inner race or outer race)of a bearing, cutting and grinding are carried out as described inPatent Literature 1. For example, in a method of manufacturing(processing) the outer race, processes illustrated in FIG. 4 aresequentially carried out.

First, as illustrated in FIG. 4A, an outer race blank W1 that isprocessed into an almost finished shape of an outer race is obtained byforging such as cold rolling. The blank W1 is quenched in a heatingfurnace 52 to be subjected to surface hardening as illustrated in FIG.4B, and then width grinding illustrated in FIG. 4C and outer diametergrinding illustrated in FIG. 4D are carried out on the blank W1. Next,the blank W1 subjected to the outer diameter grinding is turned, andthen as illustrated in FIG. 4E, a rolling surface 51 a and seal grooves51 b are processed into desired shapes. Finally, as illustrated in FIG.4F, the rolling surface 51 a is superfinished using a grindstone 53.Thus, the blank W1 is completed as an outer race 51.

The same processes are carried out also in a case of manufacturing(processing) the inner race. That is, an inner race blank that isprocessed into an almost finished shape of an inner race is obtained byforging such as cold rolling. The blank is quenched in a heating furnaceto be subjected to surface hardening, and then width grinding is carriedout on the blank. Next, the blank subjected to the width grinding isturned, and then a rolling surface and seal grooves of the blank areprocessed into desired shapes. Inner diameter grinding is performed onthe blank thus cut, and superfinishing is performed on the rollingsurface of the blank using a grindstone. Thus, the inner race blank iscompleted as an inner race.

CITATION LIST

-   Patent Literature 1: JP 06-246546 A

SUMMARY OF INVENTION Technical Problems

That is, the method illustrated in FIG. 4 has the following lead timeafter heat treatment: heat treatment→width grinding→cutting→grinding.This is because, when a bearing to be manufactured has a large size (hasan inner diameter dimension of 180 mm or more), the bearing issignificantly deformed after the heat treatment, and thus requires alarge finishing allowance.

Accordingly, the above-mentioned method has a lot of processingprocesses, which leads to an increased working time period. Further,after the cutting, chucking of a workpiece is temporarily released, andre-chucking is carried out for grinding. Thus, in a case of carrying outthe re-chucking after temporarily releasing the chucking, it isnecessary to perform an alignment work again, which causes a problem inworkability. Accordingly, the workpiece may sometimes be misaligned, andhence in order to absorb this misalignment, it is necessary to preparean extra machining allowance for grinding.

Further, in a case where it is necessary to remove a large machiningallowance when grinding, processing is performed using a roughgrindstone with good efficiency. However, when the processing isperformed using the rough grindstone, a required surface property is notobtained, and it is necessary to carry out super finishing (mirrorgrinding) on the rolling surface.

In addition, at the time of cutting, a damaged layer having a thicknessof several tens of micrometers, which is called a whiter layer or aheat-affected layer, is generated on the workpiece, and hence it isimpossible to finish a region for receiving high stress, such as arolling surface of a bearing.

Therefore, in view of the above-mentioned circumstances, the presentinvention provides a processing method capable of shortening a lead timewithout the need for carrying out super finishing (mirror grinding), andprovides a bearing manufactured using the processing method.

Solution to Problems

A processing method of the present invention is a processing method ofcarrying out finishing of a component of a bearing while chucking thecomponent by a chucking device, the processing method comprisingcarrying out hardened steel cutting and grinding while chucking thecomponent without releasing the chucking by the chucking device. Thehardened steel cutting merely means cutting. Cutting is normally carriedout on a raw material. Accordingly, in order to define that the cuttingof the present invention is cutting performed after heat treatment(after quenching), the cutting of the present invention is referred toas hardened steel cutting.

According to the processing method of the present invention, thehardened steel cutting and the grinding are carried out while chuckingthe component. Therefore, between the hardened steel cutting and thegrinding, it is unnecessary to attach and detach a workpiece(component). Thus, it is unnecessary to perform an alignment work whenre-chucking. Hence, an occurrence of misalignment can be prevented, anda machining allowance for grinding can be made small.

It is preferred that the component comprise a rolling surface, andfinish grinding of the rolling surface and cutting of other regionsexcept the rolling surface be carried out simultaneously. In this case,the cutting (hardened steel cutting) may be performed in a state inwhich a machining allowance of 100 μm or less remains on a single-sidedsurface of the component as a finish grinding allowance of the rollingsurface.

The component may comprise an inner race having an outer surface onwhich the rolling surface is formed, and the component may comprise anouter race having an inner surface on which the rolling surface isformed.

A first bearing of the present invention uses the inner race processedby the above-mentioned processing method. Further, a second bearing ofthe present invention uses the outer race processed by theabove-mentioned processing method.

Advantageous Effects of Invention

According to the processing method of the present invention, themachining allowance can be made small, and a grinding stone can beselected while placing more emphasis on accuracy than on efficiency. Asa result, it is possible to obtain a surface property required as aproduct, and to omit super finishing (mirror grinding) of the rollingsurface and the like. Thus, it is possible to shorten a lead time, andto improve productivity. In particular, according to the presentinvention, the machining allowance can be made small, and hence theprocessing method of the present invention is preferred for componentsof a large-sized bearing that is greatly deformed after the heattreatment (for example, bearing having an inner diameter dimension of180 mm or more). Further, the hardened steel cutting is performed as drycutting, and hence a grinding coolant is not needed. Accordingly, thehardened steel cutting is eco-friendly, and in addition, has anadvantage that a workpiece can be finished with high dimensionalaccuracy.

The finish grinding of the rolling surface and the cutting of otherregions except the rolling surface are carried out simultaneously, andthus more efficient processing can be carried out. Further, the cutting(hardened steel cutting) is performed in a state in which the machiningallowance of 100 μm or less remains on the single-sided surface of thecomponent as the finish grinding allowance of the rolling surface, andthus a damaged layer does not remain in a product. As a result, it ispossible to provide a high-quality product.

According to the above-mentioned processing method, each component canbe formed by processing performed for a shortened lead time. Whenassembling a bearing using the component thus formed, it is possible toimprove productivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A cross-sectional view illustrating an inner race of a bearing tobe processed by a processing method according to the present invention.

FIG. 2 A cross-sectional view illustrating an outer race of the bearingto be processed by the processing method according to the presentinvention.

FIG. 3 A cross-sectional view illustrating the bearing to be processedby the processing method according to the present invention.

FIG. 4A A view illustrating outer race blank processing of aconventional method of processing an outer race of a bearing.

FIG. 4B A view illustrating surface finishing of the conventional methodof processing an outer race of a bearing.

FIG. 4C A view illustrating width grinding of the conventional method ofprocessing an outer race of a bearing.

FIG. 4D A view illustrating outer diameter grinding of the conventionalmethod of processing an outer race of a bearing.

FIG. 4E A view illustrating profiling of the conventional method ofprocessing an outer race of a bearing.

FIG. 4F A view illustrating finishing of the conventional method ofprocessing an outer race of a bearing.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of the present invention is described withreference to FIGS. 1 to 3.

FIG. 3 illustrates a cross-sectional view of a bearing (tapered rollerbearing) using components processed by a processing method according tothe present invention. The bearing comprises: an inner race 2 having anouter surface on which a conical rolling surface 2 a is formed; an outerrace 3 having an inner surface on which a conical rolling surface 3 a isformed; tapered rollers 4 interposed between the rolling surface 2 a ofthe inner race 2 and the rolling surface 3 a of the outer race 3; and aretainer 5 for retaining the tapered rollers 4. The inner race 2comprises a small collar portion 2 b on a small diameter side of therolling surface 2 a, and a large collar portion 2 c on a large diameterside of the rolling surface 2 a. Note that, components to be processedby the processing method of the present invention comprise the innerrace 2 and the outer race 3.

Regarding the processing method according to the present invention, acase of the inner race 2 is first described. According to the processingmethod, heating treatment is carried out on an inner race forming blank(blank that is almost finished into a product shape) 2A (see FIG. 1). Asthe heating treatment, for example, quenching can be performed in aheating furnace. Then, width grinding is carried out, and as illustratedin FIG. 1, cutting and grinding are carried out. The inner race formingblank 2A has an outer surface on which a conical rolling surface formingsurface 2Aa is formed, and comprises a small collar portion 2Ab on asmall diameter side of the rolling surface forming surface 2Aa, and alarge collar portion 2Ac on a large diameter side of the surface formingsurface 2Aa.

The cutting and the grinding are carried out while chucking the blank2A, which forms the inner race 2 as the component, without releasingchucking by a chucking device 10. The chucking device 10 can be formedof, for example, a magnetic chuck.

The cutting is carried out using a cutting tool 11, and the grinding iscarried out using a grinding tool 12. Using the cutting tool 11,hardened steel cutting is carried out. Accordingly, the cutting tool 11comprises a cutter 15 capable of performing the hardened steel cutting.The cutter 15 capable of performing the hardened steel cutting can beformed of, for example, a sintered tool that is obtained by adding aspecial ceramic binder to Cubic Boron Nitride (CBN). The cutter 15described above is commercially available. The cutter 15 is supported bya support 14, and can be moved by a moving mechanism (not shown) in atleast an arrow “A” direction and an arrow “B” direction that areparallel to an axial center of the inner race 2. Herein, the hardenedsteel cutting merely means cutting. Cutting is normally carried out on araw material. Accordingly, in order to define that the cutting of thepresent invention is cutting performed after heat treatment (afterquenching), the cutting of the present invention is referred to ashardened steel cutting.

The grinding tool 12 comprises a disk-like grindstone 16, and a drivingmechanism 17 for rotating the grindstone 16 about an axial center of thegrinding tool 12. The driving mechanism 17 comprises, for example, adriving motor 18, and a transmission shaft 19 for transmitting arotational driving force of the driving motor 18 to the grindstone 16.The axial center of the grinding tool 12 is inclined in accordance withan inclination angle of the rolling surface 2 a of the inner race 2.Further, the grinding tool 12 can be moved in such an inclined state inan arrow “C” direction and an arrow “D” direction.

The chucking device 10 comprises abase table 20 on which the inner raceforming blank 2A is attracted, and can rotate and drive the base table20. In this case, on the base table 20, an end surface 2Ad on a largethickness side of the inner race forming blank 2A is placed and fixed.Thus, the inner race forming blank 2A attracted on the base table 20 isdriven so as to rotate about an axial center O of the base table 20. Forexample, the base table 20 is placed and fixed on an existing rotarytable that is publicly known and used, and thus the base table 20 can berotated about the axial center O thereof.

Accordingly, while rotating the base table 20 about the axial center Othereof in an arrow “E” direction, as illustrated in FIG. 1, the cutter15 of the cutting tool 11 is positioned on a radially inner side of theinner race forming blank 2A and on a side opposite to the base table,and then moved in the arrow “A” direction. In this way, it is possibleto perform the cutting (hardened steel cutting) on the inner surface ofthe inner race forming blank 2A, and to finish the inner surface of theinner race 2. In this case, the cutting is performed in a state in whicha machining allowance of 100 μm or less remains on a single-sidedsurface of the blank as a finish grinding allowance of the rollingsurface 2 a.

When carrying out this cutting, the grinding using the grinding tool 12is carried out. At this time, as illustrated in FIG. 1, the grindingtool 12 is arranged on a radially outer side of the inner race formingblank 2A in a state in which an axial center Oa of the grinding tool 12is inclined in accordance with an inclination angle of the rollingsurface forming surface 2Aa. Further, in this state, while keeping thegrinding tool 12 at this inclination angle, the grindstone 16 is rotatedabout the axial center Oa thereof and moved close to the inner raceforming blank 2A in the arrow “C” direction, and then an outerperipheral surface of the grindstone 16 is brought into contact with therolling surface forming surface 2Aa. In this way, it is possible tocarry out the grinding on the rolling surface forming surface 2Aa, andto finish the rolling surface 2 a of the inner race 2.

Next, a method of processing the outer race 3 is described. Also in thiscase, after forming an outer race forming blank (blank that is almostfinished into a product shape) 3A, heating treatment is carried out onthe blank 3A. As the heating treatment, for example, quenching can beperformed in a heating furnace. Then, width grinding is carried out, andcutting (hardened steel cutting) and grinding are carried out. The outerrace forming blank 3A has an inner surface on which a conical rollingsurface forming surface 3Aa is formed. In the chucking device 10, a basetable 30 comprises an annular support portion 30 a on an outerperipheral portion of an upper surface of the base table 30. On thesupport portion 30 a, an end surface 3Ab on a large thickness side ofthe outer race forming blank 3A is placed and fixed.

Accordingly, while rotating the base table 30 about an axial center O1thereof in an arrow “F” direction, as illustrated in FIG. 2, the cutter15 of the cutting tool 11 is positioned on a radially outer side of theouter race forming blank 3A and on a side opposite to the base table,and then moved in an arrow “A1” direction. In this way, it is possibleto perform the cutting (hardened steel cutting) on the outer surface ofthe outer race forming blank 3A, and to finish the outer surface of theouter race 3.

When carrying out this cutting, the grinding using the grinding tool 12is carried out. At this time, as illustrated in FIG. 2, the grindingtool 12 is arranged on a radially inner side of the outer race formingblank 3A in a state in which the axial center Oa of the grinding tool 12is inclined in accordance with an inclination angle of the rollingsurface forming surface 3Aa. Further, in this state, while keeping thegrinding tool 12 at this inclination angle, the grindstone 16 is rotatedabout the axial center Oa thereof and moved close to the inner surfaceof the outer race forming blank 3A in an arrow “D1” direction, and thenthe outer peripheral surface of the grindstone 16 is brought intocontact with the rolling surface forming surface 3Aa. In this way, it ispossible to carry out the grinding on the rolling surface formingsurface 3Aa, and to finish the rolling surface 3 a of the outer race 3.The cutting is performed in a state in which a machining allowance of100 μm or less remains on a single-sided surface of the blank as afinish grinding allowance of the rolling surface 3 a.

By the way, a grinding stone consists of three elements (abrasive grain,binder, and pore) and five factors (type of abrasive grains, grain size,grade, structure, and binder). Here, the three elements representelements forming a grindstone, and the five factors represent propertiesof those elements. The abrasive grain means a highly hard granular orpowdered substance exerting a function as a grindstone. The binder meansa material functioning as a bonding material for bonding and retainingabrasive grains to one another, and is also referred to as a bond. Thepore means a space present in a grinding stone, and has a function ofstoring chips.

Regarding the type of abrasive grains, JIS R6111-2002 (artificialabrasive) prescribes properties of general abrasive grains forindustrial use, and the abrasive grains can be roughly classified intoalumina-based abrasive grains and silicon carbide-based abrasive grains.In relation to a workpiece to be applied, the alumina-based abrasivegrains are suitable for metals such as general steel and tool steel, andthe silicon carbide-based abrasive grains are suitable for a nonferrousmetal and a non-metal such as aluminum, copper, and cemented carbide.The grain size refers to a size of abrasive grains, and is expressed bya screen mesh number. When the grain size is expressed numerically,values equal to or smaller than 220 express coarse grains, and valueslarger than 220 express fine powders. The smaller numerical valuesexpress coarser grains, and coarser grains have lower strength. Thegrain size is selected depending on finishing accuracy of a surface tobe ground. However, there is no relation between a finished surfaceroughness and the grain size, and the finished surface roughness variesdepending on a dressing condition. The grade is represented by letters Ato Z as an index indicating a retaining force between the abrasive grainand the binder. A letter closer to A represents a softer grade. Ingeneral, a soft grindstone is used for a hard workpiece, and a hardgrindstone is used for a soft workpiece. Further, a grindstone having ahigher grade has higher strength, and a grindstone having a softer gradehas lower strength. The structure is expressed as an index determinedbased on a proportion of abrasive grains of a grindstone per unit volume(percentage of grain). Percentages of grain ranging from 62% to 34% areclassified into fifteen classes that are numerically expressed by 0 to14. When the percentage of grain is 62%, the structure is expressed as0. The binder refers to a material for bonding abrasive grains to oneanother.

Accordingly, as the above-mentioned grindstone 16 of the grinding tool12, various grindstones can be selected based on the above-mentionedthree elements and five factors depending on a material and the like ofthe inner race 2 or the outer race 3 to be ground.

According to the processing method of the present invention, thehardened steel cutting and the grinding are carried out while chuckingthe component. Therefore, between the cutting (hardened steel cutting)and the grinding, it is unnecessary to attach and detach a workpiece(component). Thus, it is unnecessary to perform an alignment work whenre-chucking. Hence, an occurrence of misalignment can be prevented, andthe machining allowance for grinding can be made small. With this, thegrinding stone can be selected while placing more emphasis on accuracythan on efficiency. As a result, it is possible to obtain a surfaceproperty required as a product, and to omit super finishing (mirrorgrinding) of the rolling surface and the like. Thus, it is possible toshorten a lead time, and to improve productivity. In particular,according to the present invention, the machining allowance can be madesmall, and hence the processing method of the present invention ispreferred for components of a large-sized bearing that is greatlydeformed after the heat treatment (for example, bearing having an innerdiameter dimension of 180 mm or more). Further, the hardened steelcutting is performed as dry cutting, and hence a grinding coolant is notneeded. Accordingly, the hardened steel cutting is eco-friendly, and inaddition, has an advantage that a workpiece can be finished with highdimensional accuracy.

Finish grinding of the rolling surfaces 2 a, 3 a and cutting of otherregions except the rolling surfaces 2 a, 3 a are carried outsimultaneously, and thus more efficient processing can be carried out.Further, the cutting (hardened steel cutting) is performed in a state inwhich the machining allowance of 100 μm or less remains on thesingle-sided surface of the blank as the finish grinding allowance ofthe rolling surface 2 a or the rolling surface 3 a, and thus a damagedlayer does not remain in a product. As a result, it is possible toprovide a high-quality product.

According to the above-mentioned processing method, each component canbe formed by processing performed for a shortened lead time. Whenassembling a bearing using the component thus formed, it is possible toimprove productivity.

By the way, the above-mentioned embodiment exemplifies the taperedroller bearing as a bearing, but another bearing such as a deep grooveball bearing or an angular contact ball bearing may be employed. Here,regarding the deep groove ball bearing, a raceway groove formed in aninner race or an outer race has a circular arc cross-section that isslightly larger in radius than a rolling ball. It is possible to apply aradial load as well as axial loads in both directions. The deep grooveball bearing has a low friction torque, and is suitable for partsrotating at high speed and applications requiring low noise and lowvibration. The angular contact ball bearing is a bearing in which a ballis held in contact with a raceway of an inner race or a raceway of anouter race at some angle in a radial direction. The application of theaxial load is limited in one direction, but the angular contact ballbearing is suitable for receiving a combined load of the axial load andthe radial load. This bearing has a contact angle, and hence an axialcomponent force is generated when the radial load acts. Accordingly, theangular contact ball bearing can be used in opposed arrangement of twobearings or in combination of multiple bearings. In a case of mountingtwo bearings adjacently, there are obtained matched angular contact ballbearings that are set through adjusting a clearance previously. Notethat, regarding the tapered roller bearing, a tapered roller and abearing ring are held in line-contact with each other, and a design ismade so that an inner race rolling surface, an outer race rollingsurface, and a cone vertex of the roller coincide with one point on arotation center line of the bearing. Thus, the roller receives aresultant force from the inner race rolling surface and the outer racerolling surface to roll on the rolling surfaces while being pressedagainst and guided by a cone back face rib of the inner race. Further,it is possible to apply the radial load and the axial load in onedirection. As the contact angle becomes larger, a load capacity for theaxial load is increased. Even in a case of receiving a pure radial load,the axial component force is generated, and hence the tapered rollerbearing is normally used in opposed arrangement of two bearings.

The embodiment of the present invention is described above, but thepresent invention is not limited to the above-mentioned embodiment andvarious modifications can be made thereto. For example, as the heattreatment performed before the cutting and the grinding, various methodssuch as carburizing and quenching, and immersion quenching can be useddepending on a material and the like of the blank. Further, variouschanges can be made in rotational speed at the time of the cutting andthe grinding of the inner race forming blank 2A or the outer raceforming blank 3A, moving speed of the cutter 15 at the time of thecutting using the cutting tool 11, rotational speed of the grindstone 16of the grinding tool 12, and the like. Further, as the chucking device10, any device may be employed as long as the device can chuck aworkpiece (component) to be processed and can perform the hardened steelcutting and the grinding while keeping this chucking state. Thus, thechucking device 10 is not limited to the magnetic chuck, and it ispossible to use another existing device that is publicly known and used.

In the above-mentioned processing processes illustrated in FIGS. 1 and2, the component is exemplified as a component of the tapered rollerbearing, but in a case where the component is a rolling bearing asillustrated in FIG. 4, the cutting tool 11 or the grinding tool 12 has adifferent configuration, moving direction, and the like. However, inthis case, it is possible to use the cutting tool 11 or the grindingtool 12 having an existing configuration, moving mechanism, and the likethat are publicly known and used.

INDUSTRIAL APPLICABILITY

It is possible to carry out super finishing (mirror grinding). Apart tobe processed by the processing method comprises an inner race and anouter race of a deep groove ball bearing, an angular contact ballbearing, a tapered roller bearing, or the like. As the chucking devicefor holding a workpiece (component) at the time of cutting and grinding,there can be used a magnetic chuck for attracting and fixing a magneticmaterial by magnetism. Examples of the magnetic chuck include a typeusing a permanent magnet, a type using an electromagnet, and a hybridtype using both a permanent magnet and an electromagnet.

REFERENCE SIGNS LIST

-   -   2 inner race    -   2 a rolling surface    -   3 outer race    -   3 a rolling surface    -   10 chucking device

1-7. (canceled)
 8. A bearing comprising an inner race, the inner raceincluding: an outer surface; and an inner surface, wherein the innerrace is heat treated, the outer surface includes a hardened rollingsurface, the hardened rolling surface is hardened steel cut to have amachining allowance of 100 μm or less remaining as a finish grindingallowance and finish ground to remove a damaged layer generated by thehardened steel cutting of the hardened rolling surface, the innersurface is hardened steel cut, and the hardened steel cutting of theinner surface occurs simultaneously with the finish grinding of thehardened rolling surface.
 9. A bearing comprising an outer race, theouter race including: an outer surface; and an inner surface, whereinthe outer race is heat treated, the inner surface includes a hardenedrolling surface, the hardened rolling surface is hardened steel cut tohave a machining allowance of 100 μm or less remaining as a finishgrinding allowance and finish ground to remove a damaged layer generatedby the hardened steel cutting of the hardened rolling surface, the outersurface is hardened steel cut, and the hardened steel cutting of theouter surface occurs simultaneously with the finish grinding of thehardened rolling surface.